An electromagnetic motor provided with a field magnetic (permanent magnet) has been in heavy usage in a wiper system of a vehicle as a drive source of the wiper system. Such a motor is used even under a low temperature range of about −40° C. depending on the use condition of a vehicle or the like and, therefore, is required to operate normally even under the low temperature environment. That is, the motor is required to be activated without difficulty from a low temperature state in which the motor is almost frozen and to allow a wiper or the like to operate in the same way as at room temperature.
However, the motor is kept under a low temperature environment, the resistance of a copper wire serving as an armature winding becomes smaller, so that a current easily flows to the winding. Accordingly, when the motor may become overloaded under a low temperature environment and locked, a winding current (lock current) becomes significantly large, with the result that the field magnet is easily demagnetized. For example, when a swinging wiper arm is brought into contact with an obstacle such as snow existing near its lower reverse position to allow the motor to be in a locked state immediately after the motor is activated under a low temperature environment, a lock current increases, with the result that the field magnet may be demagnetized. Especially, in the case of a ferrite series magnet, the coercivity of the field magnet itself is easily lowered at low temperature time, so that demagnetization under a low temperature environment becomes increasingly prominent. When the magnet is demagnetized, not only is the motor output decreased but also there is a possibility that it becomes impossible to obtain desired motor characteristics even if ambient temperature is brought back to room temperature.    Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 7-39062    Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 11-122703